Neuronal Expression of UBQLN2(P497H) Exacerbates TDP-43 Pathology in TDP-43(G348C) Mice through Interaction with Ubiquitin

Mutations in the gene encoding ubiquilin-2 (UBQLN2) are linked to amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). UBQLN2 plays a central role in ubiquitin proteasome system (UPS) and UBQLN2 up-regulation exacerbates TDP-43 cytoplasmic aggregates. To analyze interaction between UBQLN2 and TDP-43 and to produce a relevant ALS animal model, we have generated a new transgenic mouse expressing UBQLN2(P497H) under the neurofilament heavy (NFH) gene promoter. The UBQLN2(P497H) mice were then bred with our previously described TDP-43(G348C) mice to generate double-transgenic UBQLN2(P497H); TDP-43(G348C) mice. With low-expression levels of UBQLN2, the double-transgenic mice developed TDP-43 cytosolic accumulations in motor neurons starting at 5 months of age. These double-transgenic mice exhibited motor neuron loss, muscle atrophy, as well as motor and cognitive deficits during aging. The microglia from double-transgenic mice were hyperresponsive to intraperitoneal injection of lipopolysaccharide (LPS). In vivo and in vitro analyses suggested that extra UBQLN2 proteins can exacerbate cytoplasmic TDP-43 accumulations by competing with the UPS for binding to ubiquitin. Thus, increasing the pool of ubiquitin promoted the UPS function with ensuing reduction of TDP-43 cytosolic accumulations. In conclusion, the double-transgenic UBQLN2(P497H); TDP-43(G348C) mice provides a unique mouse model of ALS/FTD with enhanced TDP-43 pathology that can be exploited for drug testing. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s12035-018-1411-3) contains supplementary material, which is available to authorized users.